<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>队列应用</title>
</head>
<body>
    <script>
        class Queue{  //步骤2
            constructor(content=[]){  
                //步骤3  constructor本身里面接收的是它的内容，默认起名为content。且为空数组
                this._queue=[...content];  
                //里面加一个名字为_queue的属性，且后面为复制过来的数组再传递给它
            }
            shift(){   //步骤5
                const value = this._queue[0];
                this._queue.shift();
                return value;
            }
            push(n){   //步骤7
                this._queue.push(n);
                return this._queue.length;
            }
        }

        var q = new Queue([1,2,3,4])    //步骤1
        q.shift();  //步骤4  有返回值
        q.push(6);  //步骤6  有返回值
        console.log(q._queue);
    </script>
    
</body>
</html>